diff --git a/adminer/include/adminer.inc.php b/adminer/include/adminer.inc.php
index 0dee1711..e87b7c35 100644
--- a/adminer/include/adminer.inc.php
+++ b/adminer/include/adminer.inc.php
@@ -121,9 +121,9 @@ class Adminer {
 		echo "<table cellspacing='0' class='layout'>\n";
 		echo $this->loginFormField('driver', '<tr><th>' . lang('System') . '<td>', html_select("auth[driver]", $drivers, DRIVER, "loginDriver(this);") . "\n");
 		echo $this->loginFormField('server', '<tr><th>' . lang('Server') . '<td>', '<input name="auth[server]" value="' . h(SERVER) . '" title="hostname[:port]" placeholder="localhost" autocapitalize="off">' . "\n");
-		echo $this->loginFormField('username', '<tr><th>' . lang('Username') . '<td>', '<input name="auth[username]" id="username" value="' . h($_GET["username"]) . '" autocomplete="username" autocapitalize="off">' . script("focus(qs('#username')); qs('#username').form['auth[driver]'].onchange();"));
+		echo $this->loginFormField('username', '<tr><th>' . lang('Username') . '<td>', '<input name="auth[username]" id="username" value="' . h((isset($_GET["username"]) ? $_GET["username"] : "")) . '" autocomplete="username" autocapitalize="off">' . script("focus(qs('#username')); qs('#username').form['auth[driver]'].onchange();"));
 		echo $this->loginFormField('password', '<tr><th>' . lang('Password') . '<td>', '<input type="password" name="auth[password]" autocomplete="current-password">' . "\n");
-		echo $this->loginFormField('db', '<tr><th>' . lang('Database') . '<td>', '<input name="auth[db]" value="' . h($_GET["db"]) . '" autocapitalize="off">' . "\n");
+		echo $this->loginFormField('db', '<tr><th>' . lang('Database') . '<td>', '<input name="auth[db]" value="' . h((isset($_GET["db"]) ? $_GET["db"] : "")) . '" autocapitalize="off">' . "\n");
 		echo "</table>\n";
 		echo "<p><input type='submit' value='" . lang('Login') . "'>\n";
 		echo checkbox("auth[permanent]", 1, $_COOKIE["adminer_permanent"], lang('Permanent login')) . "\n";
@@ -968,13 +968,15 @@ class Adminer {
 <?php
 		if ($missing == "auth") {
 			$output = "";
-			foreach ((array) $_SESSION["pwds"] as $vendor => $servers) {
-				foreach ($servers as $server => $usernames) {
-					foreach ($usernames as $username => $password) {
-						if ($password !== null) {
-							$dbs = $_SESSION["db"][$vendor][$server][$username];
-							foreach (($dbs ? array_keys($dbs) : array("")) as $db) {
-								$output .= "<li><a href='" . h(auth_url($vendor, $server, $username, $db)) . "'>($drivers[$vendor]) " . h($username . ($server != "" ? "@" . $this->serverName($server) : "") . ($db != "" ? " - $db" : "")) . "</a>\n";
+			if (isset( $_SESSION["pwds"])) {
+				foreach ((array) $_SESSION["pwds"] as $vendor => $servers) {
+					foreach ($servers as $server => $usernames) {
+						foreach ($usernames as $username => $password) {
+							if ($password !== null) {
+								$dbs = $_SESSION["db"][$vendor][$server][$username];
+								foreach (($dbs ? array_keys($dbs) : array("")) as $db) {
+									$output .= "<li><a href='" . h(auth_url($vendor, $server, $username, $db)) . "'>($drivers[$vendor]) " . h($username . ($server != "" ? "@" . $this->serverName($server) : "") . ($db != "" ? " - $db" : "")) . "</a>\n";
+								}
 							}
 						}
 					}
diff --git a/adminer/include/auth.inc.php b/adminer/include/auth.inc.php
index 8669351f..3183b51a 100644
--- a/adminer/include/auth.inc.php
+++ b/adminer/include/auth.inc.php
@@ -51,7 +51,7 @@ function check_invalid_login() {
 	}
 }
 
-$auth = $_POST["auth"];
+$auth = (isset($_POST["auth"]) ? $_POST["auth"] : null);
 if ($auth) {
 	session_regenerate_id(); // defense against session fixation
 	$vendor = $auth["driver"];
@@ -76,7 +76,7 @@ if ($auth) {
 		redirect(auth_url($vendor, $server, $username, $db));
 	}
 
-} elseif ($_POST["logout"] && (!$has_token || verify_token())) {
+} elseif (isset($_POST["logout"]) && $_POST["logout"] && (!$has_token || verify_token())) {
 	foreach (array("pwds", "db", "dbs", "queries") as $key) {
 		set_session($key, null);
 	}
diff --git a/adminer/include/bootstrap.inc.php b/adminer/include/bootstrap.inc.php
index 01a9d0b6..ef72d915 100644
--- a/adminer/include/bootstrap.inc.php
+++ b/adminer/include/bootstrap.inc.php
@@ -1,6 +1,7 @@
 <?php
-function adminer_errors($errno, $errstr) {
-	return !!preg_match('~^(Trying to access array offset on value of type null|Undefined array key)~', $errstr);
+function adminer_errors($errNo, $errStr, $errFile, $errLine) {
+	file_put_contents("php://stderr", sprintf("%d - %s - %s:%d\n", $errNo, $errStr, $errFile, $errLine));
+	printf("%d - %s - %s:%d\n", $errNo, $errStr, $errFile, $errLine);
 }
 
 error_reporting(6135); // errors and warnings
@@ -30,7 +31,7 @@ if (isset($_GET["file"])) {
 	include "../adminer/file.inc.php";
 }
 
-if ($_GET["script"] == "version") {
+if (isset($_GET["script"]) && $_GET["script"] == "version") {
 	$fp = file_open_lock(get_temp_dir() . "/adminer.version");
 	if ($fp) {
 		file_write_unlock($fp, serialize(array("signature" => $_POST["signature"], "version" => $_POST["version"])));
@@ -46,10 +47,10 @@ if (!$_SERVER["REQUEST_URI"]) { // IIS 5 compatibility
 if (!strpos($_SERVER["REQUEST_URI"], '?') && $_SERVER["QUERY_STRING"] != "") { // IIS 7 compatibility
 	$_SERVER["REQUEST_URI"] .= "?$_SERVER[QUERY_STRING]";
 }
-if ($_SERVER["HTTP_X_FORWARDED_PREFIX"]) {
+if (isset($_SERVER["HTTP_X_FORWARDED_PREFIX"]) && $_SERVER["HTTP_X_FORWARDED_PREFIX"]) {
 	$_SERVER["REQUEST_URI"] = $_SERVER["HTTP_X_FORWARDED_PREFIX"] . $_SERVER["REQUEST_URI"];
 }
-$HTTPS = ($_SERVER["HTTPS"] && strcasecmp($_SERVER["HTTPS"], "off")) || ini_bool("session.cookie_secure"); // session.cookie_secure could be set on HTTP if we are behind a reverse proxy
+$HTTPS = (isset($_SERVER["HTTPS"]) && $_SERVER["HTTPS"] && strcasecmp($_SERVER["HTTPS"], "off")) || ini_bool("session.cookie_secure"); // session.cookie_secure could be set on HTTP if we are behind a reverse proxy
 
 @ini_set("session.use_trans_sid", false); // protect links in export, @ - may be disabled
 if (!defined("SID")) {
@@ -102,8 +103,16 @@ if ($adminer->operators === null) {
 	$adminer->operator_regexp = $operator_regexp;
 }
 
-define("SERVER", $_GET[DRIVER]); // read from pgsql=localhost
-define("DB", $_GET["db"]); // for the sake of speed and size
+if (isset($_GET[DRIVER])) {
+	define("SERVER", $_GET[DRIVER]); // read from pgsql=localhost
+} else {
+	define("SERVER", "");
+}
+if (isset($_GET["db"])) {
+	define("DB", $_GET["db"]); // for the sake of speed and size
+} else {
+	define("DB", "");
+}
 define("ME", preg_replace('~\?.*~', '', relative_uri()) . '?'
 	. (sid() ? SID . '&' : '')
 	. (SERVER !== null ? DRIVER . "=" . urlencode(SERVER) . '&' : '')
diff --git a/adminer/include/functions.inc.php b/adminer/include/functions.inc.php
index 6565375a..37f17714 100644
--- a/adminer/include/functions.inc.php
+++ b/adminer/include/functions.inc.php
@@ -595,7 +595,10 @@ function stop_session($force = false) {
 * @return mixed
 */
 function &get_session($key) {
-	return $_SESSION[$key][DRIVER][SERVER][$_GET["username"]];
+	if (isset($_GET["username"]) && isset($_SESSION[$key][DRIVER][SERVER][$_GET["username"]])) {
+		return $_SESSION[$key][DRIVER][SERVER][$_GET["username"]];
+	}
+	return null;
 }
 
 /** Set session variable for current server
@@ -630,7 +633,10 @@ function auth_url($vendor, $server, $username, $db = null) {
 * @return bool
 */
 function is_ajax() {
-	return ($_SERVER["HTTP_X_REQUESTED_WITH"] == "XMLHttpRequest");
+	if (isset($_SERVER["HTTP_X_REQUESTED_WITH"])) {
+		return ($_SERVER["HTTP_X_REQUESTED_WITH"] == "XMLHttpRequest");
+	}
+	return false;
 }
 
 /** Send Location header and exit
diff --git a/adminer/include/lang.inc.php b/adminer/include/lang.inc.php
index 0122da6a..16f7f774 100644
--- a/adminer/include/lang.inc.php
+++ b/adminer/include/lang.inc.php
@@ -63,7 +63,7 @@ function get_lang() {
 */
 function lang($idf, $number = null) {
 	global $LANG, $translations;
-	$translation = ($translations[$idf] ? $translations[$idf] : $idf);
+	$translation = (isset($translations[$idf]) ? $translations[$idf] : $idf);
 	if (is_array($translation)) {
 		$pos = ($number == 1 ? 0
 			: ($LANG == 'cs' || $LANG == 'sk' ? ($number && $number < 5 ? 1 : 2) // different forms for 1, 2-4, other
@@ -102,10 +102,10 @@ if (isset($_POST["lang"]) && verify_token()) { // $error not yet available
 }
 
 $LANG = "en";
-if (isset($langs[$_COOKIE["adminer_lang"]])) {
+if (isset($_COOKIE["adminer_lang"]) && isset($langs[$_COOKIE["adminer_lang"]])) {
 	cookie("adminer_lang", $_COOKIE["adminer_lang"]);
 	$LANG = $_COOKIE["adminer_lang"];
-} elseif (isset($langs[$_SESSION["lang"]])) {
+} elseif (isset($_SESSION["lang"]) && isset($langs[$_SESSION["lang"]])) {
 	$LANG = $_SESSION["lang"];
 } else {
 	$accept_language = array();